<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>

        div{
            width: 100px;
            height: 100px;
            margin: 0 auto;
            border: 5px solid rebeccapurple;
            /* border-top-left-radius: 100px;
            border-top-right-radius: 100px;
             */
             /* 
                半圆
                宽高成两倍
             border-radius: 100px 100px 0 0; */

                /* 扇形需要正方形 */
                /* border-radius: 0 100px 0 0 ; */

                

        }

    </style>
</head>
<body>
    
    <div>


    </div>

</body>
</html>